Stable oil-in-water emulsions have been a problem in many areas of the petroleum industry. In the production of oil under water-flood conditions, oil-in-water emulsions are obtained from the production wells. These emulsions must be broken in order to recover the oil in useful form. When cleaning oil tanker bilges, oil-in-water emulsions frequently form and present disposal problems. In the processing of crude oils, such as by desalting, stable emulsion layers are formed in the desalter resulting in the waste of valuable oil and the creation of a disposal problem. Oily wastewater streams that are generated at many different refinery processing units often contain solids that are intermixed with hazardous organic materials that are regulated under the Resource, Conservation and Recovery Act (RCRA). The hazardous organic materials must be separated from the solids before the solids can be land disposed or land treated.
The stability of oil-in-water emulsions such as those described above is increased by the presence of dispersed solids. It is recognized that the stability of oil-water-solids emulsions is a function of the composition, i.e., the relative amounts of oil, water and solids in the mixture as well as the type of oil and solids. The breaking of such emulsions requires alteration of this ratio. The addition of miscible hydrocarbons to water-in-oil generally only serves to swell the emulsion phase and does not lead to emulsion breaking. Thus, simple techniques such as diluting the emulsion with naphtha do not lead to the desired result. Removal of solids by filtration has a tendency to break the emulsion, but generally, since the emulsions are so viscous, filtration is extremely difficult. Centrifugation of oil-water-solid emulsions results in rather poor separation.
U.S. Pat. No. 2,235,639 describes a procedure for the resolution of oil and water emulsions by adding a liquefied gas (such as ethane, butane, propane, etc.) to the emulsion. The liquefied gas is added to the emulsion under sufficient pressure to prevent vaporization of the gas. While the mixture is under pressure, the emulsion breaks, and water settles from the emulsion leaving the oil in a purified condition. While still under pressure, water is withdrawn and the oil is transferred to a secondary zone where it is heated to volatilize the hydrocarbon gas.
U.S. Pat. Nos. 2,383,362 and 2,383,363 describe processes for the separation of water from hydrocarbon-water emulsions. More particularly, these patents relate to the breaking of tar emulsions and the separation of the water from the tar component by mixing a liquefied normally gaseous hydrocarbon solvent with the emulsions. The '362 patent is directed primarily to the use of propane whereas the '363 patent utilizes pentane as the liquid phase hydrocarbon.
U.S. Pat. No. 3,696,021 describes the separation of oily sludges by mixing the sludges with a light hydrocarbon to form an oil-hydrocarbon phase and a water-solids phase. The oil-hydrocarbon phase then is heated to an elevated temperature to remove the light hydrocarbons which may be recycled, and the oil is recovered for further use. The light hydrocarbons disclosed as being suitable for use in the process include propane, butane, pentane, as well as mixtures and isomers thereof.